Apparatus and method for decomposition of chemical compounds using a self-supporting member

ABSTRACT

An apparatus for and method of decomposing a chemical compound, which may be an environmentally undesirable material, is accomplished by impinging a flow of the chemical compound on a heated member. Various embodiments are possible, including having the member have a plurality of openings, having the member be configured to direct the flow of the chemical compound in a particular direction, and having the member be self supported on the wall of the reaction chamber.

This application is related to co-pending applications having AttorneyDocket Nos. 08/235,626, 08/236,913, and 08/235,609, all filedconcurrently on 29 Apr. 1994.

This application is related to co-pending applications having AttorneyDocket Nos. 08/235,626, 08/236,913, and 08/235,609, all filedconcurrently on 29 Apr. 1994.

BACKGROUND OF THE INVENTION

This invention relates, in general, to decomposition of chemicalcompounds, and more particularly, but not limited to, an apparatus andmethod for decomposing a chemical compound into environmentallyacceptable materials.

Chemical compounds, in particular, environmentally undesirable materials(which can include hazardous materials), such as halogenated organiccompounds or volatile organic compounds, are widely used in manymanufacturing areas as reactive agents, solvents, and refrigerants.

As is well known, these environmentally undesirable materials aredetrimental to people and the environment by generating harmfulsubstances and/or destroying the stratospheric ozone layer and/or bygenerating global warming effects. Although these environmentallyundesirable materials are widely used in industrial, chemical,automotive, and pharmaceutical industries, it is clear that either theuse of these materials must be stopped or severely limited, or thedestruction of such materials must be improved in order to comply withincreasing regulations.

In many manufacturing situations, it is impossible to stop using manyenvironmentally undesirable materials because no substitute materialswhich are environmentally acceptable are available at the present time.Thus, an efficient, cost effective method of decomposing environmentallyundesirable materials to environmentally acceptable and/or non-hazardousmaterials is not only necessary to be in compliance with anti-pollutionregulations and to protect the environment, but necessary to continuemanufacturing many products which require the use of environmentallyunacceptable materials.

In the past, there were three prevalent techniques to decompose or alterenvironmentally undesirable materials to environmentally acceptablematerials. The first method involves using a radio frequency (RF)induced plasma reaction to decompose the environmentally undesirablematerials. However, a method using solely an RF plasma induced reactionhas not been proven to be effective in destroying some environmentallyundesirable materials at the desired efficiency levels, nor has it beenproven to be cost effective. Currently available units can not destroyhalogenated organic compounds with suitable efficiencies. One of thedisadvantages of this method is that it is difficult to maintain theplasma in a controlled fashion to destruct environmentally undesirablematerials.

A second method of destroying environmentally undesirable materialsincludes combustion of the environmentally undesirable material.Combustion techniques have extremely low efficiency due to burning of agreat amount fuel in the form of hydrogen or hydrocarbons. In addition,combustion can not be performed in a vacuum, thus, vacuum pumps used inmanufacturing must be subjected to the environmentally undesirablematerials, which increases the maintenance of the vacuum pumps. In somesituations, it would be desirable to destroy the environmentallyundesirable materials under a vacuum to avoid exposure of theenvironmentally undesirable materials to vacuum pumps.

A third method of decomposing environmentally undesirable materialsinvolves transforming environmentally undesirable materials into liquidform by cryopumping. The liquid form of the environmentally undesirablematerials are recoverable, but still environmentally unsafe and requirerisk through handling and transportation. Disadvantages of this methodare that it is very expensive and maintenance intensive. In addition,the cryopumping apparatus has a large footprint. A large amount of spacewhere the environmentally undesirable materials are produced is notavailable in many manufacturing situations. In addition, a potentiallydangerous situation can arise if cryopumping is utilized where there isa potential to condense compounds which are pyrophoric in condensed formand are still hazardous materials. Due to this danger, cryopumping isnot an alternative in many industries.

The efficiency target for destruction of environmentally undesirablematerial such as halogenated organic compounds is 80% or greater. Noneof the methods described above provide this efficiency level in a costeffective manner. Thus, it would be desirable to destroy environmentallyundesirable material using an efficient, cost effective method.

SUMMARY OF THE INVENTION

An apparatus for and method of decomposition of a chemical compoundcomprises a reaction chamber comprised of a wall and having a first endand a second end and having an inlet for receiving a chemical compoundand an outlet at the second end, a member positioned in the reactionchamber, the member being self-supported on the wall above the secondend of the reaction chamber, an energy source capable of generating anenergy to heat the member, and a conduit physically coupled to the inletof the reaction chamber for directing the flow of a chemical compoundtowards the member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of an embodiment of the presentinvention;

FIG. 2 illustrates an embodiment of a portion of the present invention;

FIG. 3 illustrates an embodiment of a member utilized in the presentinvention;

FIG. 4 illustrates an embodiment of a portion of the present invention;

FIG. 5 illustrates another embodiment of a member utilized in thepresent invention;

FIG. 6 illustrates another embodiment of a member utilized in thepresent invention;

FIG. 7 illustrates another embodiment of a portion of the presentinvention;

FIG. 8 illustrates another embodiment of a portion of the presentinvention;

FIG. 9 illustrates another embodiment of a portion of the presentinvention; and

FIG. 10 illustrates an embodiment of an application where the presentinvention can be utilized.

DETAILED DESCRIPTION OF THE DRAWINGS

An apparatus for and method of decomposing or reacting a chemicalcompound 70, which may be an environmentally undesirable material, toend product(s) 77, which are desirably environmentally acceptablematerials, or materials which can be further utilized before conversioninto environmentally acceptable materials is presented.

FIG. 1 illustrates a simplified schematic view of an embodiment of anapparatus of the present invention. A housing 10 is provided to house areaction chamber 20. An energy source 60 may be positioned inside oroutside of housing 10. An energy 62 is generated from energy source 60and is transferred to reaction chamber 20. A portion of the walls ofreaction chamber 20 must transmit energy 62 produced by energy source60. An example of this is a window comprised of quartz and formed inreaction chamber 20. The walls of housing 10 should be comprised of amaterial which contains energy 62 from energy source 60. Stainless steelis one example of such a material. Housing 10 has an inlet 12 and anoutlet 14 which are physically coupled to an inlet 22 and an outlet 24,respectively, of reaction chamber 20. Inlet 22 and outlet 24 of reactionchamber 20 are shown as openings in the wall of reaction chamber 20.

Reaction chamber 20 provides a reaction zone for the destruction ordecomposition of chemical compound 70. Chemical compound 70 is definedas a chemical compound(s) in a gaseous state. Examples of chemicalcompound 70 are halogenated organic compounds, hydrides, or volatileorganic compounds which may be generated by a processing tool 82. Anexample of processing tool 82 is an RF plasma deposition or etch toolused in semiconductor processing.

Chemical compound 70 must be introduced toward or impinge member 30 todecompose chemical compound 70 at suitable efficiencies. When chemicalcompound 70 is decomposed it can then react with a reactive material(disclosed below) provided in reaction chamber 20 to form an endproduct(s) 77. End product 77 is comprised of decomposed portions ofchemical compound 70. End product 77 is desirably an environmentallyacceptable material. End product 77 exits through outlet 24 and aconduit 50 which is physically coupled to outlet 24 of reaction chamber20. End product 77 may be exhausted to the atmosphere after exitingthrough conduit 50 or may be run through a scrubber system, where aportion of end product 77 will react with another material which canthen be released to the atmosphere. Scrubber systems are well known inthe art.

In certain applications, it may be desirable or necessary to have thereaction chamber subjected to a vacuum. A vacuum can be provided inreaction chamber 20 by a vacuum pump 79 physically coupled to conduit50. Thus, reaction chamber 20 may be placed between processing tool orequipment 82 which generates chemical compound 70 and vacuum pump 79.Vacuum pump 79 can be the same pump that is already utilized in manyprocesses downstream from processing tool 82 which produces chemicalcompounds that operate in a vacuum.

Operation of the present invention may be at down in the 100 millitorrrange or above. However, an advantage of the present invention is thatoperation may also take place up around 100-500 torr. Although operationmay take place above this level, safety requirements realisticallyprevent the operation of this type of apparatus at or above atmosphericpressure (760 torr). The prior art pure RF plasma method of destroyingchemical compound discussed before is only capable of running in themillitorr range, rather than torr range, because you have to be belowone torr to maintain an RF plasma without having to introduce othercostly means of maintaining the RF plasma, such as hydrogen fuel.

The size of reaction chamber 20 is important; reaction chamber 20 shouldbe large enough so that the residence time of chemical compound 70 issufficient to allow destruction of chemical compound 70. Typically, thefootprint of the apparatus of the present invention is small enough thatit can be utilized adjacent to the equipment which produces chemicalcompound 70 or as part of roof scrubber systems.

The inside of the wall of reaction chamber 20 is preferably comprised ofa material which does not substantially react with chemical compound 70or end product 77. The wall of reaction chamber 20 (excluding theportion which transmits energy 62) may be either transparent or opaqueto radiant energy, e.g., the energy given off from the reactions takingplace in reaction chamber 20 and energy radiating from a member 30(described below).

A transparent wall may be comprised of quartz. A transparent wallprovides a means for some radiant energy to escape. It is believed thatwhen destroying some types of chemical compounds 70, allowing some ofthe radiant energy to escape provides for driving the reaction towardsthe end products, end product 77. If some of the radiant energy is heldin the reaction chamber, the reaction may be driven the other way,towards chemical compound 70. In the case where the walls of reactionchamber 20 are comprised of quartz, no substantial reaction takes placebetween chemical compound 70 and the quartz of the reaction wallsbecause chemical compound 70 has already been broken down and reactedwith a portion of member 30 to form end product 77, and/or in oneembodiment, quartz does not inductively couple with energy 62 of energysource 60, therefore, it remains cool (relative to the temperature ofmember 30), which does not provide for the necessary heat to decomposechemical compound 70 near its surface.

An opaque wall may be comprised of a metal, which does not couple withenergy 62 of energy source 60, with a radiant energy absorption coating,such as steel or aluminum with black anodized or black manganese oxidecoatings. It is believed that an opaque wall will absorb and transfersome radiant energy from reaction chamber 20 and drive the reaction toend product 77. In addition, the metal of the opaque wall provides forcorrosion resistance not found in some other materials.

Member 30 is positioned within reaction chamber 20. Member 30 is a plateand is comprised of a material that can be heated by energy source 60.In a preferred embodiment, the portion of member 30 which is heated isheated to a temperature of approximately 200°-1400° C. It is believedthat temperatures below 200° C. will not decompose most chemicalcompounds 70. Temperatures above 1400° C. are not desirable because theywill start to melt materials used herein. The shape, size, andcomposition of various embodiments of member 30 is disclosed below.Member 30 may be positioned in reaction chamber 20 by a supportstructure 35. Support structure 35 is comprised of a material which canwithstand the temperatures in reaction chamber 20. Quartz is an exampleof what support structure 35 may be made of. Another support means isillustrated and described below.

Some kind of reactive material is desirably provided in reaction chamber20 in order to react with decomposed chemical compound 70 so thatdecomposed chemical compound will not recombine. An optional feature ofthe present invention is the introduction of a reactive material 90 intoreaction chamber 20. Reactive material 90 may be provided through aninlet 80 provided through housing 10 and into reaction chamber 20.Alternatively, reactive material 90 may be mixed with chemical compound70 prior to entering reaction chamber 20 through conduit 48. In someprocesses, reactive material 90 may be generated from tool 82 inconjunction with chemical compound 70.

Reactive material 90 is a material which reacts with chemical compound70 to form all or a portion of end product 77. Reactive material 90 canbe an oxidizing or reducing agent, such as for example, water vapor,oxygen, ammonia, hydrogen, methane, or nitrous oxide which will reactwith chemical compound 70. An example of a reaction of chemical compound70, C₂ F₆, with H₂ O is as follows: C₂ F₆ +O₂ +H₂ O->CO₂ +HF. Ifreactive material 90 is utilized, then the impinged surface of member 30may or may not be comprised of a material which does not react withchemical compound 70.

Energy source 60 is preferably an electric heat generator, althoughother means, such as an electron beam may be used. The use or combustionof fuels or use of electron beams to heat member 30 is undesirable froma cost, safety, and cleanliness standpoint. A combustion process is notdesirable because it also creates undesirable end products. When energysource 60 is comprised of an electric heat generator, at least a portionof member 30 must be electrically heated by energy source 60 to atemperature greater than or equal to 200° C.

Most preferably, energy source 60 is comprised of a microwave energysource. A microwave energy source is preferable because it is believedthat the molecular vibration of chemical compound 70 by microwave energyin combination with chemical compound 70 receiving heat from member 30is necessary to destruct some chemical compounds 70. It is furtherbelieved that a microwave energy source, rather than other forms ofdielectric heating done at lower frequencies, is necessary to destructcertain chemical compounds 70 that will not be destroyed at suitableefficiency levels by using other energy sources having a frequency rangelower than 0.9 GHz. It is believed that C₂ F₆ can not be decomposed atsuitable efficiency levels without the use of microwave energy. Where amicrowave energy source is not required for decomposition, a microwaveenergy source is still preferable because of its low cost, bothoperational and capital.

The microwave energy source preferably operates at a power of 100 to5,000 watts and a microwave frequency of 0.9-10 GHz. A frequency of 2.45GHz is most preferred because of cost and it has been federallyauthorized for commercial use. When a microwave energy source is used,it is desirable to have energy source 60 external to housing 10 andenergy 62 supplied through a waveguide 65 into reaction chamber 20 asshown in FIG. 1.

When a microwave energy source is used, member 30 must be comprised of amaterial which inductively couples with the microwave energy. A materialwhich inductively couples with microwave energy will be directly heatedby the microwave energy to a temperature equal to or greater than 200°C. Examples of suitable materials that inductively couple to microwaveenergy source are lead, zinc, tin, antimony, silver, iron, titanium,nickel and cobalt or any alloy thereof. Other materials may couple witha microwave energy source, but may not be suitable because they aretoxic or have other undesirable properties, such as vaporizing at thetemperatures of operation. Examples of materials that do not inductivelycouple with microwave energy are copper, gold, silicon, quartz, otherglasses, and ceramics. Materials that do not inductively couple withmicrowave energy can be doped with materials that do inductively couplewith microwave energy. For example, member 30 may be comprised ofsilicon carbide doped with any of the above materials which couple withmicrowave energy.

The manner in which chemical compound 70 is introduced into reactionchamber 20 is critical to the invention. Chemical compound 70 isintroduced into the reaction chamber so that chemical compound 70bombards or impinges against member 30 so that hot wall reactions cantake place. If member 30 is shaped in a plate configuration having twomajor surfaces as shown in FIG. 1, then it is preferable to have member30 be positioned such that the major surface of member 30 which isimpinged by chemical compound 70 is not substantially parallel to theflow of chemical compound 70. Another way to state this is to have themajor surface of member 30 positioned substantially perpendicular to theflow of chemical compound 70.

Optimally, the flow of chemical compound 70 is introduced into thereaction chamber so that chemical compound 70 bombards or impingesagainst member 30 having a solid impinged surface when chemical compound70 is comprised of halogenated organic compounds, for example.Halogenated organic compounds have higher activation energies than, forexample, volatile organic compounds such as alcohols, and are believedto require the physical collisions to reach suitable decompositionefficiencies.

In the embodiment shown in FIG. 1, conduit 40 is physically coupled toinlet 12 of reaction chamber 20 and inlet 24 of housing 10. Conduit 40has an end 42 coupled to a processing tool 82 where chemical compound 70is generated and an exit end 44 where chemical compound 70 exits intoreaction chamber 20. Conduit 40 provides for introducing chemicalcompound 70 into reaction chamber 20 by restricting the flow of chemicalcompound 70 as it exits into reaction chamber 20 to a confined portionof reaction chamber 20 and directing the flow towards member 30. Theportion of conduit 40 which is inside reaction chamber 20 should becomprised of a material which is transparent to energy 62 from energysource 60, such as quartz. The portion of conduit 40 which is outside ofreaction chamber 20 can be comprised of, for example, stainless steel.The inside cross-sectional area of conduit 40 is dependent on thedesired flow rate of chemical compound 70, among other things. Thepurpose of having conduit 40 extend into reaction chamber 20 is todirect the flow towards member 30 and when energy source 60 is comprisedof microwave energy, to expose chemical compound 70 to microwave energybefore and during impingement of chemical compound 70 on member 30. Thisexposure may be required to decompose certain chemical compounds 70 atsuitable efficiencies.

To obtain optimum destruction of chemical compound 70, exit end 44 ispositioned as close as possible to member 30. This position is notnecessarily preferred because it is desirable to have a nonrestrictiveflow of chemical compound 70 where chemical compound 70 does notbackflow into processing tool 82. A minimum distance 73 between exit end44 of conduit 40 and the major surface of member 30 towards whichchemical 70 is introduced is preferably the distance where the flow rateof chemical compound 70 is not altered, i.e., so that the introductionof chemical compound 70 towards member 30 is transparent to processingtool 82 which generated chemical compound 70. This minimum distance canalso be calculated as the distance where the inside cross-sectional areaof conduit 40 is equal to the escape surface area, which is defined asthe length of the perimeter of the inside cross-sectional area ofconduit 40 multiplied by the distance from exit end 44 and the impingedsurface of member 30. This is preferred so that no chemical compound 70back flows into processing tool 82 which generated chemical compound 70and possibly contaminate processing tool 82.

As stated above, chemical compound 70 must be introduced toward orimpinge member 30 to obtain decomposition efficiency levels of a minimumof 80%. The surface of member 30 on which chemical compound 70 isintroduced must be in the path of the flow of chemical compound 70. Exitend 44 must be close enough to the major surface of member 30, as shownby distance 73, to at least allow for the transfer of heat by conductionof heat and/or radiation of heat from member 30 to chemical compound 70,otherwise, destruction of chemical compound 70 will not take place at anefficiency level of greater than 80%.

Exit end 44 should not be placed at a distance greater than the distanceaway from the member where sufficient hot wall reactions of the chemicalcompound will take place to decompose the chemical compound at anefficiency level of a minimum of 80%. The distance where theintroduction of chemical compound 70 towards member 30 is transparent toprocessing tool 82 multiplied by 2 is believed to be the maximumdistance where destruction efficiencies of 80% or greater will beobtained.

Another way to define this maximum distance is the distance where theescape surface area is equal to the cross-sectional area of conduit 40multiplied by 2. It is believed that placing exit end 44 of conduit 40further than this maximum distance will allow too much of chemicalcompound to not make physical contact with member 30 and/or not allowchemical compound 70 to receive heat from member 30, and thereforedecomposition efficiencies above 80% will never be achieved.

Exact distances 73 between exit end 44 and member 30 where suitabledestruction efficiency is obtained will vary according to variousparameters, such as the flow rate of chemical compound 70, thecomposition of chemical compound 70, and the temperature of member 30,among other parameters. Once the critical parameters are defined, oneskilled in the art can design the reaction zone appropriately accordingto the present invention.

For the present invention to have the desired efficiencies ofdestruction of chemical compound 70, energy source 60 must supply enoughenergy to heat member 30 to allow destruction of chemical compound 70 atthe desired efficiency levels when heat is received by chemical compound70 from member 30, with or without a plasma (explained further below)induced reaction of chemical compound 70 in reaction chamber 20.

The physical collision of chemical compound 70 against member 30, whilechemical compound 70 is hot from receiving heat from member 30 may benecessary to cause the molecules of some forms of chemical compound 70,such as halogenated organic compounds, to break. When chemical compound70 is comprised of compounds that can ignite, the receipt of heat frommember 30 is believed to be all that is necessary to cause ignition andtherefore destruction at suitable efficiency levels. Even in this case,to achieve the desired efficiencies, it is still necessary to introducethe flow of chemical compound 70 towards member 30 so that chemicalcompound 70 can receive heat from member 30.

In certain applications, it may be desirable to also generate a plasmawithin reaction chamber 20. The present invention may operate at anacceptable efficiency level without the use of a plasma, oralternatively, member 30 provides enough radiant energy to maintain theplasma during operation, without the use of other fuels. In thedestruction of halogenated organic compounds, it is believed that aplasma may be necessary, because it weakens and breaks bonds when otherforms of destruction are inefficient. There are many ways known in theart to generate plasmas. A plasma is generated when gases such as oxygenor nitrogen are excited by energy 62 of energy source 60. These gasesmay be supplied in reaction chamber through conduit 48 into conduit 40,for example.

FIG. 2 illustrates the operation of the present invention. only aportion of the present is shown for illustrative convenience. Inoperation, a flow of chemical compound 70 moves through conduit 40 (asshown by the arrow) toward member 30 in a environment exposed to, in oneembodiment, microwave energy absorption and resonance. As the gasmolecules of chemical compound 70 impinge on member 30, the temperatureof chemical compound 70 is elevated and then condensed owing tocollision pressure against member 30. The temperature and gas densityincrease until detonation of chemical compound 70 is achieved. Thedetonation of chemical compound 70 directs the flow of at least aportion of the detonated chemical compound 70 gases back into a portionof conduit 40 by virtue of the positioning of member 30 in the path ofthe flow of chemical compound 70. It is believed that this brings aboutthe ability for the apparatus of the present invention to have a higherefficiency of decomposition of chemical compound 70 by reworkingpartially decomposed chemical compound 70 and/or end product 77 as thesedetonations which cause an overall pressure variation which does notcause backflow into processing tool 82, create microsecond repeatingdetonation waves which keep the molecules of chemical compound 70reworking and recycling from the impinged surface of member 30 and intoa portion of conduit 40 to enhance residence time of chemical compound70, resulting in achievable high efficiencies of decomposition. Thedetonation rebound and rework of chemical compound 70 by a surfaceimpinged, heated member 30 does not take place in, for example, packedbed reactors. In packed bed reactors, molecules are not reworked backacross the same path as they are in the present invention.

For some chemical compounds 70, this detonation rebound and rework ofchemical compound 70 by a thermally heated member 30 by itself, withoutmicrowave resonance, will make significant efficiency improvements overexisting non-surface impinging, radiant thermal decomposition methods.

FIGS. 3-9 illustrate various embodiments of member 30. FIG. 3illustrates a first embodiment of member 30. Here, member 30 iscomprised of a material 100 which is heated by energy 62 of energysource 60. The total mass of material 100 should be in large enough toprovide adequate absorption and radiation of heat. In this embodiment,the surface of member 30 on which chemical compound 70 is introduced iscomprised of a reactive material 102 which reacts with the decomposedchemical compound 70 to form end product 77. Reactive material 102 whichreacts with chemical compound 70 can be, for example quartz, silicondioxide (SiO₂), graphite, ceramics, or aluminum oxides. An example of areaction of chemical compound 70, C₂ F₆, with SiO₂ is as follows: C₂ F₆+SiO₂ ->CO₂ +SiF₄. It is not required that member 30 be comprised of amaterial which is reactive with chemical compound 70 if a reactivematerial 90 is provided as shown in FIG. 1.

It is believed that in order to obtain the desired destructionefficiencies, the surface of member 30 on which chemical compound 70 isintroduced must have at least the same area as the cross-sectional areaof the flow of chemical compound 70, i.e., the cross-sectional area ofthe opening at exit end 44 of conduit 40. Member 30 is desirably atleast 2 times larger than the cross-sectional area of conduit 40 so thatthe residence time of 70 is adequate to start breakdown destructionreactions occurring. The impinged surface of member 30 may have anyshape.

FIG. 4 illustrates a second embodiment of member 30. only a portion ofthe apparatus is shown for illustrative convenience. Here, member 30 isconfigured to direct more of the flow of chemical compound 70 intoreaction chamber 20 back toward and behind exit end 44 of conduit 40. Inthis embodiment, member 30 is shown to have a curved shape. In thismanner, the residence time of chemical compound 70 may be increased. Theconfiguration increases the residence time of chemical compound 70before flowing out through outlet 50 so that optimum destruction andconversion to end product 77 can take place.

FIG. 4 also illustrates an embodiment where a plurality of members 30may be used. Reaction chamber 20 has a first end and a second end;outlet 50 is positioned at the second end and the first end is oppositethe second end. Additional members 31 may be positioned at the first endbehind exit end 44 of conduit 40 in the path of chemical compound 70.Members 31 are the same as member 30. Preferably, additional members 31are positioned at the first end by a support structure 36. Supportstructure 36 can be comprised of the same material as support structure35, however, support structure 36 must be attached to the walls ofreaction chamber 20 and member 31 must be attached to support structure36. The method of attachment will depend on what support structure 36and reaction chamber 20 are comprised of. The manner in which supportstructure 36 is attached to the walls of reaction chamber 20 and member31 is attached to support structure 36 is not critical to the invention,and may be carried out by many different means. In this way, chemicalcompound 70, as shown by flow illustrated in FIG. 3, can receiveadditional heat by conduction and radiation from additional members 31.

FIG. 5 illustrates another embodiment where member 30 is configured todirect the flow of chemical compound 70 into reaction chamber 20 backtowards exit end 44 of conduit 40. In this embodiment, member 30 isshown to have a sidewall 104 formed as the ends of member 30. Sidewall104 can be anywhere to that it is not planar with the major surface ofmember 30 and directs the flow of chemical compound 70 into reactionchamber 20 back towards exit end 44 of conduit 40. FIG. 5 onlyillustrates the configuration where sidewall 104 is substantiallyperpendicular to the major surface of member 30.

FIG. 6 illustrates another embodiment of member 30. Here, member 30 isconfigured to optimize the destruction of chemical compound 70 comprisedof volatile organic compounds (VOC's). VOC's is typically have a loweractivation energy than halogenated organic compounds, and thus willrequire less energy to destroy. In addition, the residence time does notneed to be as high as the residence time of halogenated organiccompounds. In this instance, it is desirable to have member 30 have aplurality of openings 32 therethrough. A mesh configuration is shown inFIG. 6 as an example, however, many other configurations are possible. Awire mesh configuration can be used and may be desirable from thestandpoint of cost and convenience to use because a wire mesh can belightweight.

In this case, a plurality of members 30 may be used as is shown in FIG.7 (two members 30 are shown) in highly simplified form. The advantage ofusing a member 30 having a plurality of openings 32 is that residencetime may be decreased, but chemical compound 70 will still receive heatfrom member 30 by conduction and radiation. In this embodiment, more ofthe heat received will be in the form of radiation from member 30,rather than conduction from member 30 compared to using a member 30having a solid surface.

When a plurality of members 30 are used, a variety of positions arepossible. The second (or subsequent members) member 30 may be positionedso that all or a portion of chemical compound 70 which did not makephysical contact with the first member 30 will physically contact thesecond member 30 (as shown in FIG. 7). Alternatively, second member 30may be positioned in direct alignment with first member 30, where theopenings of the first member 30 line up with the openings of the secondmember 30, so that the portion of chemical compound 70 which did notmake physical contact with first member 30 will not make physicalcontact with second member 30.

FIGS. 8 and 9 illustrate an embodiment of a way to support member 30 isreaction chamber 20. FIG. 8 illustrates a side view, while FIG. 9illustrates a top view. In this embodiment, member 30 and reactionchamber 20 are configured so that member 30 is self supported inreaction chamber 20. Member 30 is shown having a square shape, and thewall of reaction chamber 20 is shown having a circular shape. Othershapes which allow self support are possible. Note that the walls ofreaction chamber 20 may be tapered so that placement of member 30 inreaction chamber 20 is facilitated. In this embodiment, the surface areaof member 30 should leave enough through space 106 in reaction chamber20 so that end product 77 can exit through outlet 50 without risk ofback flow of end product 77 or chemical compound 70 through conduit 40to processing tool 82. The advantages of this self supporting scheme areits simplicity, reduced cost, and reduced maintenance.

EXAMPLE 1

An example is described to illustrate the specific advantages of thepresent invention over the prior art, and is not intended to be alimitation of the present invention. A specific example of destructionof chemical compound 70 comprised of a C₂ F₆ will be described, withreference to FIG. 1.

Reaction chamber 20 is placed in the exhaust vacuum line between theequipment producing C₂ F₆ and a vacuum source such as vacuum pump 79shown in FIG. 1. In this particular example, reaction chamber 20 is avertical reactor having an approximate volume of 10 liters. Reactionchamber 20 runs idle at approximately 25 millitorr and in operation, inthis embodiment, at approximately 500-600 millitorr. In this example,the footprint of the apparatus is only approximately 18×23".

Member 30 is comprised of a metal doped substrate which inductivelycouples to energy 62 of energy source 60 and heats up to a desiredtemperature. Examples of what member 30 may be comprised of are ceramicswith layers of zinc, arsenic and tin or silicon with layers oftitanium-nickel-silver formed therein, typically each less than 1 micronthick. Member 30 is approximately horizontally positioned in the middleof reaction chamber 20. The position of member 30 is the vertically inreaction chamber 20 is determined by the desired residence time. Theimpinged surface of member 30 is approximately two times larger than thecross-sectional area of conduit 40.

Conduit 40 is a circular tube having an inside diameter of approximately100 millimeter (mm). Exit end 44 of conduit 40 is positionedapproximately over the center of member 30 and a distance of 25 mm awayfrom the impinged surface of member 30 so that the flow rate of C₂ F₆ isconstant.

In this example, energy source 60 is a microwave energy source operatingat 2.45 GHz and 750 Watts which emits microwave energy 62 through atleast a portion of reaction chamber 20. Member 30 is heated to atemperature of approximately 200°-900° C.

The C₂ F₆ is introduced into reaction chamber 20 at a flow rate ofapproximately 1.5 liters per minute. A reactive material 90 comprised ofoxygen is provided at approximately 1.5 liters per minute. The C₂ F₆strikes member 70, member 30 imparts heat to the C₂ F₆. A hot wallreaction can then take place against member 30; a chemical reactionbetween the C₂ F₆ and oxygen takes place to form end products 77 asfollows: C₂ F₆ +O₂ ->CO₂ +F⁻. F⁻ represents various forms of fluorinewhich may be present. In this example, the residence time of the C₂ F₆in reaction chamber 20 is approximately 500 milliseconds or less.

Efficiencies of decomposition were demonstrated to be greater than 90%removal of C₂ F₆. As stated earlier, this level of efficiency has notbeen able to be achieved by other means in a cost effective way. The useof the present invention therefore allows the decomposition ofenvironmentally undesirable materials which are required to be used inmany manufacturing settings.

EXAMPLE 2

With reference to FIG. 10, an example of an application where the systemof the present invention can be utilized to decompose a chemicalcompound 200 and react with a reactive material to form an end product205, and then use decomposed chemical compound 205 to clean a processingtool 250. A simplified schematic of this application is shown in FIG.10. For example, processing tool 250 can be a Low Pressure ChemicalVapor Deposition (LPCVD) tool used to deposit material such aspolysilicon (Si), silicon dioxide (SiO₂) or silicon nitride (SiN_(x)) onsemiconductor wafers. In this type of equipment, deposition of thesematerials also takes place on the walls of a reaction tube in which thesemiconductor wafers are placed. It is desirable to clean the surface ofthe reaction tube to avoid particulate contamination of thesemiconductor wafers.

Chemical compound 200 is supplied through conduit 40 in reaction chamber20. In this example, chemical compound 205 is comprised of nitrousfluoride (NF₃) or perfluorocompounds (PFC's, such as C₂ F₆ or CF₄) mixedwith oxygen (O₂). Oxygen is the reactive material which reacts withchemical compound 205 to form end product 205. Member 30 is comprised ofa material which can be heated and preferably has a configuration asshown in FIG. 6 if NF3 is used, but a solid member 30 is preferred ifPFC's are used. After chemical compound 200 is introduced toward thesurface of member 30 to decompose, an example of a reaction which cantake place using NF3 is as follows: NF₃ +O₂ ->NO₂ +F⁻. In thisembodiment, NO₂ and F⁻ comprise an end product 205. Here, it isdesirable to have end product 205 be comprised of F⁻, which is veryreactive when it exits reaction chamber 20. Therefore, no reactivematerials that will react with F⁻ should be provided in reaction chamber20. End product 205 is exhausted through conduit 50, which is physicallycoupled to reaction chamber 20. Conduit 50 is physically coupled to aprocessing tool 250 which has a surface that needs to be cleaned. Forthe example given here, the following reactions can take place inprocessing tool 250 to form end products 210 as follows:

F⁻ +Si->SiF₄

F⁻ +SiN_(x) ->SiF₄ +N_(x)

F⁻ +SiO₂ ->SiF₄ +O₂

The end products 210 of the above reactions are exhausted out ofprocessing tool 250 through a conduit 255 which is physically coupled toa vacuum pump 260 and out to the atmosphere or a collection chamber (notshown).

The advantage of cleaning performed using the present invention is thatcleaning may be done in situ, i.e., without removing the portion (thereaction tube) of processing tool that needs to be cleaned.

We claim:
 1. An apparatus for decomposition of a chemical compound,comprising:a reaction chamber comprised of a wall and having a first endand a second end and having an inlet for receiving a chemical compoundand an outlet at the second end; a member having a major face andpositioned in the reaction chamber, the member being self-supported onthe wall above the second end of the reaction chamber without othermeans of support; an energy source capable of generating an energy toheat the member; and a conduit physically coupled to the inlet of thereaction chamber for directing the flow of a chemical compound towardsthe member, wherein the major face of the member is not positionedsubstantially parallel to the flow of the chemical compound from theconduit.
 2. The apparatus of claim 1 wherein the wall of the reactionchamber is circular and the member has a shape having at least fourcorners so that the at least four corners of the member rest on aportion of the wall to support the member.
 3. The apparatus of claim 1wherein the member is configured to provide an opening to the second endof the reaction chamber.
 4. The apparatus of claim 1 wherein the memberis comprised of a material which can be heated to a temperature equal toor greater than 200° C.
 5. The apparatus of claim 1 wherein the memberis comprised of silicon carbide doped with a material which can beheated by the energy source.
 6. The apparatus of claim 1 wherein themember is comprised of a reactive material and a material which can heheated by the energy source.
 7. The apparatus of claim 6 wherein thereactive material is comprised of SiO₂.
 8. The apparatus of claim 1wherein the wall of the reaction chamber is circular and the wall istapered so that the first end has a larger diameter than the second end.9. The apparatus of claim 1 wherein the member is configured to directthe chemical compound to the first end of the reaction chamber.
 10. Amethod of decomposing a chemical compound comprising the stepsof:providing an energy source which generates an energy; providing areaction chamber comprised of a wall and having a first end and a secondend and having an inlet for receiving a chemical compound and an outletat the second end; providing a member having a major face and positionedin the reaction chamber, the member being self-supported on the wallabove the second end of the reaction chamber without other means ofsupport; heating the member with the energy of the energy source; andintroducing a flow of a chemical compound into the reaction chambertowards the member, wherein the major face of the member is notpositioned substantially parallel to the flow of the chemical compound.11. The method of claim 10 wherein the step of providing the reactionchamber comprises providing a reaction chamber wherein the wall of thereaction chamber is circular and the step of providing the membercomprises providing the member having a shape having at least fourcorners so that the at least four corners of the member rest on aportion of the wall to support the member.
 12. The method of claim 10wherein the step of providing the member comprises providing the memberhaving a configuration to provide an opening to the second end of thereaction chamber.
 13. The method of claim 10 wherein the step ofproviding the member comprises providing the member comprised of amaterial which can be heated to a temperature equal to or greater than200° C.
 14. The method of claim 10 wherein the step of providing themember comprises providing the member comprised of silicon carbide dopedwith a material which can be directly heated by the energy source. 15.The method of claim 10 wherein the step of providing the membercomprises providing the member comprised of a reactive material and amaterial which can be directly heated by the energy source.
 16. Themethod of claim 15 wherein the step of providing the member comprisesproviding the member comprised of SiO₂ as the reactive material.
 17. Themethod of claim 10 wherein the step of providing the reaction chambercomprises providing the reaction chamber wherein the wall of thereaction chamber is circular and the wall is tapered such that the firstend has a larger diameter than the second end.
 18. The method of claim10 wherein the step of providing the member comprises providing themember configured to direct the chemical compound to the first end ofthe reaction chamber.
 19. A method of decomposing a chemical compoundcomprising the steps of:providing an energy source which generates anenergy; providing a reaction chamber comprised of a wall and having afirst end and a second end and having an inlet for receiving a chemicalcompound and an outlet at the second end wherein the reaction chamber iscircular and the wall is tapered so that the first end has a largerdiameter than the second end; providing a member having a major face andpositioned in the reaction chamber self supported against the wall ofthe reaction chamber without other means of support; heating the memberwith the energy of the energy source; and providing a flow of a chemicalcompound into the reaction chamber through a conduit, wherein the flowof the chemical compound exits from the conduit such that the flowimpinges on the member.
 20. The method of claim 19 wherein the step ofproviding a flow of the chemical compound further comprises adecomposition of the chemical compound taking place substantially nearthe major face of the member.